The present disclosure relates, in various embodiments, to compositions and processes suitable for use in electronic devices, such as thin film transistors (“TFT”s). The present disclosure also relates to components or layers produced using such compositions and processes, as well as electronic devices containing such materials.
Thin film transistors (TFTs) are fundamental components in modern-age electronics, including, for example, sensors, image scanners, and electronic display devices. TFT circuits using current mainstream silicon technology may be too costly for some applications, particularly for large-area electronic devices such as backplane switching circuits for displays (e.g., active matrix liquid crystal monitors or televisions) where high switching speeds are not essential. The high costs of silicon-based TFT circuits are primarily due to the use of capital-intensive silicon manufacturing facilities as well as complex high-temperature, high-vacuum photolithographic fabrication processes under strictly controlled environments. It is generally desired to make TFTs which have not only much lower manufacturing costs, but also appealing mechanical properties such as being physically compact, lightweight, and flexible. Organic thin film transistors (OTFTs) may be suited for those applications not needing high switching speeds or high densities.
The performance of a TFT can be measured by at least three properties: the mobility, current on/off ratio, and threshold voltage. The mobility is measured in units of cm2/V·sec; higher mobility is desired. A higher current on/off ratio is also desired. Threshold voltage relates to the bias voltage needed to be applied to the gate electrode in order to allow current to flow. Generally, a threshold voltage as close to zero (0) as possible is desired.
Most high-performance organic semiconductors suffer from either (1) significant degradation of their electrical properties when exposed to air; or (2) poor solution processability. Some solution-processable, high-performance polythiophene semiconductors are known for electronic device applications. For example, described in U.S. Pat. Nos. 6,770,904; 7,132,500; 7,282,733; 7,250,625; and 7,141,644 (all of which are hereby fully incorporated by reference) is the use of a semiconducting polythiophene referred to as PQT-12:

Generally speaking, the long pendant alkyl sidechains impart high solubility to the polythiophene. Excellent field-effect transistor (FET) properties have been achieved in OTFTs using this polythiophene and fabricated in ambient conditions.
PQT-12 also has a high self-assembly capability. Like most high-mobility solution-processable semiconductors, this strong self-assembly capability stems from the regioregular placement of the long pendant side-chains along the backbone, which promotes extensive lamellar ordering, as shown in FIG. 1.
However, PQT-12 is not sufficiently soluble in most common organic solvents. As a result, it requires processing in environmentally undesirable chlorinated solvents, such as chlorobenzene or dichlorobenzene, for optimal performance. Unfortunately, this also results in gelation of the solution at room temperature. This is a problem because a deposition solution is generally desired for ease of applying the polythiophene to an organic TFT. U.S. Pat. No. 6,890,868, which is hereby fully incorporated by reference, describes one solution to the gelation problem by elevating the temperature of the deposition solution. This approach still requires the use of chlorinated aromatic solvents for processing to obtain optimum performance, thus severely limiting its general application in manufacturing environments.
It would be desirable to eliminate chlorinated solvents from the manufacturing process.